Light Intensity Investigation

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Light Intensity Investigation                                                                                

Science Light Intensity Investigation


In this investigation, a controlled experiment will be conducted to determine whether the distance between an object and a light source has an effect on the intensity of light and if so, do the illuminance increase or decrease as the distance from the light source increases. Research will be formulated by conducting a controlled experiment in which we will observe the intensity of light received by a light sensor at various distances and evaluate the results gathered to determine the relationship between light intensity and distance. This phenomenon can be experienced when an oncoming car has it head lights switched on, the light intensity seems to increase as the car approaches. Similarly, the rate of photosynthesis also relies heavily on the intensity of light, as the process is seemed to be quicker when the sun’s light intensity is strong. Thus, the relationship between light intensity and distance is important to investigate so that experimental reasoning can be deducted for these phenomena’s. The intensity of the light is the amount of light that falls on a specific object. This measure is called illuminations and is expressed in Lux when the distance is measured in metric terms. A lux equals one lumen per square metre. (Anderson, 2009)


Increasing the distance of the light sensor from the light source will decrease the intensity of light (or luminance) detected by the sensor. This hypothesis is based on the knowledge that as light waves travel out from a light source in straight lines, they spread out and become less concentrated as they travel further away- making it appear dimmer. Furthermore, when an object is placed near a source, majority of the light waves emitted are concentrated on it, however when placed further back, only a small proportion of the waves are hitting it. Due to this, increasing distance ultimately decreases the illuminance (how much light from a source hits a specific object) and thus, the light intensity.


The independent variable (the variable being changed): The independent variable is going to be the distance between the light sensor and the light source (cm) with measurements varying from 10cm-100cm and increasing at 10cm increments. We will do this in order to see the effects varying distance has on light intensity. The variable will be altered by increasing the distance between the two objects by 10cm (interval length) for each set of trials. We will measure and change this gap by using a metre ruler to determine the exact distance and then we will place the light source at one end and the sensor at the determined mark on the ruler.  

The dependent variable (the variable being measured): The dependent variable is going to be the intensity of light illuminated by the light source at each particular distance (ranging from 10cm-100cm). This variable will be measured in the unit of measurement LUX. To determine the LUX illuminated at various distances, we will use Data Studio to give us accurate measurements of light hitting the light sensor that will be located at one of the ten distances, thus giving us our measurement for the particular trial.

The control variables (the variables kept the same): The other variables, which we need to keep constant, are:

  • The same conditions present around the experiment (room temperature, background light, disturbance, etc.). To ensure that the experiment is fair, we will minimize any background disturbance by conducting the experiment in a secluded area away from other groups. We will also close all blinds and switch off the room light so that there is little to no background light interfering with the light sensor’s readings. This is essential for the data’s reliability as background light can affect the readings by increasing the light intensity (lux) picked up by the sensor- more than what is being emitted by the light bulb.
  • The same strength of light being emitted from the light bulb (12 volts). To control this variable we will ensure that the tuner on the ray box is at the 12-volt (the highest) mark for all trials.
  • The same length of time each trial is conducted for (30 seconds). To keep this variable constant, we will use the clock on data studio to measure the time from the time we click the start button. The trial will finish when the virtual stopwatch reaches the 30sec mark and the stop button is clicked.
  • The same height of the light sensor above the desk. This will be controlled by using the same wooden block to place the sensor, thus ensuring that there are no changes in height of the wooden block and as a result, the light sensor.
  • The same light mode chosen on the sensor.  To control this, we will choose the sunlight mode on the light sensor and ensure that it is not changed to either of the other two buttons.
  • The same light source used. The same light bulb will be used in each trial and not changed throughout the experiment.
  • The same nozzle on the light sensor used to detect light-the front nozzle. To control this, we will place the sensor parallel to the ruler so that the front nozzle faces directly towards the light bulb and the side nozzle faces away. This is essential to ensure that we achieve accuracy as using two different nozzles would alter results as they have different levels of detecting light intensity with the side nozzle usually showing the light intensity to be significantly lower than the front nozzle.
  • The same person handling the light sensor during the experiment. Identifying one group member to handle the sensor before the experiment and then ensuring that he only handles it during each trial will control this variable.
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  • 1x 12v Light Source (or Ray Box)
  • 1x 25cm2 Wooden Block
  • 1x 25cm2 Square White Cardboard
  • 1x Light Sensor
  • 1x 1metre Ruler
  • 1x USB Link
  • 1x Laptop
  • 1x Power Supply Box
  • 1x Desk
  • 1x DC Transformer

Setup & Plan:

Here are the details of how we will conduct our experiment and the measurements we will make and process:

Our group will measure the light ...

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